Office of Radiation Safety
ORS GN15
GUIDANCE NOTES
Safe Practice for the Use of
Nuclear Density Meters
Office of Radiation Safety
Ministry of Health
PO Box 3877
Christchurch 8140
NEW ZEALAND
June 2000
Revised July 2010
© 2000,
Office of Radiation Safety
Ministry of Health
Published with the permission of the Director-General of Health
CONTENTS
Page
INTRODUCTION
LEGAL REQUIREMENTS AND RESPONSIBILITIES
1
Consents for import, export, sale and ownership
Licences to use radioactive material
Use by an unlicensed person
Responsibilities of the owner
Equipment registers and records of use
Radiation Safety Plan
1
2
3
3
4
5
SAFETY MANAGEMENT
Storage facilities
Responsibilities for storage
Labelling of the meter and its transport case
Accident prevention
Maintenance and wipe testing
Withdrawal from use
Decommissioning
Safety audits
OPERATOR SAFETY
Safety during normal use
Use by an unlicensed person
Personal monitoring
Radiation survey meters
ACCIDENTS, LOST SOURCES, AND EMERGENCIES
Accidents
Lost sources
Fire and civil defence emergencies
6
6
7
7
8
8
9
10
11
12
12
12
13
13
14
14
15
15
TRANSPORT
17
REFERENCES
18
APPENDIX
UNITS OF MEASUREMENT
Units of radioactivity
Units of radiation dose
CROSS-REFERENCE INDEX
19
19
20
21
INTRODUCTION
These Guidance notes have been written to provide information for owners and users on the
safe care and use of instruments containing radioactive materials used for the measurement of
moisture content and/or density of materials. They give practical guidance on compliance
with the requirements of radiation protection legislation and the Code of safe practice for the
use of nuclear density meters, CSP15.
Some of these instruments have been known as “soil moisture gauges” and others as “nuclear
density meters” or just “NDMs”. For simplicity, these Guidance notes will follow industry
terminology and use the term “nuclear density meter”. In the marginal notes, the
abbreviation NDM will be used.
Some parts of these Guidance notes and of the Code, CSP15 are relevant for users of
asphalt gauges containing radioactive sources. These are normally laboratory bench
instruments, and are not portable field instruments. Nevertheless, the radioactive
sources used are similar to those used for moisture measurement and the safety
implications are similar.
The units of measurement of radioactivity and radiation dose are discussed in the
Appendix.
LEGAL REQUIREMENTS AND RESPONSIBILITIES
The ownership and use of radioactive materials in New
Zealand is controlled by the Radiation Protection Act
1965[1] and the Radiation Protection Regulations 1982[2].
Importing, exporting and selling is controlled through a
consent process, and users must be licensed under the Act.
The regulations contain more detailed general requirements
for both owners and licensed users of radioactive material.
Both ownership and use of
NDMs are controlled by
law
The additional requirements specific to nuclear density
meters are contained in the Code of safe practice for the use
of nuclear density meters, CSP15. Anyone licensed to use a
nuclear density meter must comply with this Code.
CSP15 must also be
complied with
If these requirements are always fulfilled, every nuclear density meter will remain
under the responsibility of an authorised person, from the time it is imported into
New Zealand until it is exported or finally disposed of.
Consents for import, export, sale and ownership
Section 12 of the Act requires that no-one can sell, import,
or export any radioactive material (including nuclear density
meters) without having a consent to do so. An application
must be made to ORS for a consent prior to any such
transaction.
A consent from ORS is
necessary
If a nuclear density meter is being imported by a NZ agent,
then the agent must apply for a consent. If you are
importing it directly, then you must apply for a consent.
Who needs the consent?
In terms of the Act, “sale” includes lending or hiring. Any
owner must apply for a consent prior to hiring or lending
nuclear density meters to other companies or individuals.
Where a company has several branches, and circulates a
nuclear density meter around them, but maintains
responsibility for it as the owner, then this is not classed as
“loan” and is not subject to consent.
“Selling” includes lending
or hiring
If a nuclear density meter is owned by a syndicate of
independent individuals or companies, then one must be
nominated as the “owner” in terms of the legislation. In this
case a consent is necessary before it is loaned to the other
members.
One person or company
must be named as the
owner
Guidance Notes: NDMs – Legal requirements and responsibilities
1
How to get a consent form
and fee information
Forms and fee information are available on our web site:
http://www.health.govt.nz
In summary if you are:

importing a nuclear density meter directly from overseas
you need to apply for a consent;

buying a nuclear density meter from a NZ agent then it is
up to the agent to arrange for a consent;

selling, lending, or hiring out your nuclear density meter to
another company you need to apply for a consent;

transferring a nuclear density meter from one branch to
another of the same company then a consent is not
needed (but you should notify ORS of the change of
location);

exporting a nuclear density meter you need to apply for a
consent.
Licences to use radioactive material
A licence is necessary
Anyone using radioactive material for any purpose (including
a nuclear density meter) must either hold a licence for that
purpose under the Act or be acting under the supervision or
instructions of a licensee (see Section 13 of the Act). All such
licences require compliance with the Code of safe practice,
CSP15. Further specific conditions may be added in some
cases.
Obtaining a licence
information pack
A licence information pack, containing an application form for
a licence to use a nuclear density meter and copies of the Code
of safe practice CSP15, these Guidance notes, the Act, and
regulations can be obtained from ORS.
Training requirements
To be eligible for a licence an applicant must have received
training approved by ORS in all aspects of the safe handling
and management of nuclear density meters. The licence
application form includes a request for evidence of this
training. Licensees may also be required to demonstrate ongoing competency at subsequent licence renewals.
What does the term
“principal licensee” mean?
Where there is more than one licensee using the same nuclear
density meter, then each has full responsibility for safety and
compliance with all regulatory requirements while they are
using the meter. However there are some aspects of safety
management where it may be ambiguous which licensee is
responsible (eg, maintenance of a log). In this case one
licensee must be designated the “principal licensee” (see
regulation 9(3)). Some of the requirements in the Code refer
specifically to the principal licensee (see CSP15, Sections 1.3,
2.1, 2.2, 3.2.1, 3.10.1, 5.2.1).
Guidance Notes: NDMs – Legal requirements and responsibilities
2
Licensees cannot reasonably maintain control of meters
beyond a limited geographical area or in other branches
of the owner's organisation, so there should be a principal
licensee in each area or branch.
How many principal licensees
should there be?
Use by an unlicensed person (CSP15 Section 4.2)
A person who is not licensed may use a nuclear density
meter under the supervision or instructions of a licensee.
In order to ensure that it does not become too far removed
from the control of a licensed person, there must be at
least one licensee at each separate operational base or
branch of a company that uses a nuclear density meter.
Use under supervision
It is up to the licensee who is supervising to ensure the
unlicensed person is trained in all aspects of safety
necessary for the degree of independence from
supervision they will have. A person operating in the
presence of the licensee will not need as much training as
one who takes a meter away for a day to use in the
absence of the licensee.
Training is required for
unlicensed users
For short term absences (eg, annual leave) an unlicensed
person may use a meter under the licensee’s instructions
as long as the licensee can be easily contacted.
Short term absence of the
licensee
The important thing for the licensee to remember is that
they still have full legal responsibility for the safety of the
meter and they must have full confidence that the
unlicensed person knows what to do in all circumstances.
But the licensee is still
responsible
The unlicensed person must be given a set of written
instructions detailing what should be done if anything
goes wrong, and how to contact the licensee.
In case of emergency
Responsibilities of the owner
Regulation 9(1) requires the owner of a nuclear density
meter to take all reasonable steps to ensure there is
always a suitably licensed person to take care of safety.
This applies whether the meter is actually being used or
not. There must be someone on hand who is suitably
trained to ensure the meter is safely stored when not used,
that it is safely packaged and consigned when it is sent
elsewhere, and that records are properly kept. There must
be a licensee at each branch to look after the overall
management of safety. When there is more than one
licensee at a branch, then it is the responsibility of the
owner to designate one as the principal licensee (see p. 2)
to attend to these matters.
The owner must ensure there
is a licensee
Guidance Notes: NDMs – Legal requirements and responsibilities
3
Resignation or retirement
of licensee
In the event of resignation or retirement, then another
appropriate person must be designated by the owner to
apply for a licence, and there must be no interim period
without a licensee.
Storage without a licensee
If for any unforeseen reason it has not been possible to
assign a suitable licensee as required by regulation 9(1)
then the owner must either store the meter to the
satisfaction of the Director-General of Health or dispose of
it in accordance with the Regulations. If stored, the storage
facility must comply with Section 3.1 of the Code and the
owner must notify ORS of all necessary details of the
storage (see regulation 9(4)).
In the case of bankruptcy,
receivership or liquidation
A particular difficulty can arise in the case of bankruptcy,
receivership or liquidation, if a nuclear density meter is
included in the assets taken over by the administrator. A
change of ownership of this nature involves legal issues
beyond the scope of these Guidance notes. However, the
previous owner or the licensee must advise ORS of the
situation, and advise the administrator of the owner’s
obligations under regulation 9. If the licensee is still
employed then that person retains all the legal
responsibilities (see regulation 9(2)).
Owner’s responsibilities to
licensee
Most of the owner’s responsibilities are met once a licensee
has been assigned. From then on most of the legal
responsibility for compliance with the regulations and the
Code lie with the licensee. However, the owner must
provide facilities and equipment required for the safe use,
storage, transportation, or disposal as requested by the
licensee (see regulation 9(1)).
Equipment registers and records of use (CSP15 Section 2)
Importance of good record
keeping
There is a history of nuclear density meters being
misplaced, with potential significant safety consequences.
No other use of radioactive materials in New Zealand
involves the movement of radioactive sources in portable
instruments between jobs and between different responsible
licensees on a comparable scale. It is therefore vital that
complete and unambiguous records are kept of the
whereabouts of every nuclear density meter.
There is a legal
requirement for records to
be kept
Regulation 16(1) requires that anyone who has control of
any radioactive material, including a nuclear density meter,
must keep a record of the quantity, nature, and location of
them at all times.
Guidance Notes: NDMs – Legal requirements and responsibilities
4
Section 2 of the Code lists details of what must be recorded.
A record keeping system only works if it is always
followed. The Code makes it clear that every licensee using
(or responsible for the use of) a nuclear density meter is also
responsible for completing the records when it is used.
CSP15 lists requirements
There are two types of record:

A register that contains identification details of each
nuclear density meter, and where it is usually stored (see
Section 2.1 of the Code). This is like an asset register,
and gives a single check list that can be used to verify
that each meter is accounted for. Much of the
information required for the register is usually supplied
with a new meter, or can be obtained from the agent or
manufacturer.
Equipment register

A use log for each nuclear density meter (see Section
2.2 of the Code). This should enable anyone to pick a
meter listed on the register, go to the corresponding log
and find out where it has been used, who was
responsible for it, and most importantly, where it is at
the present time.
Use log
These registers and logs should be kept in a place where
they are convenient to maintain, and will not be misplaced
even if the meter is. The log should not be kept in the carrycase of the meter.
Where should records be
kept?
If a company with several branches shares a single meter (or
pool of meters), then each branch should have a log that
records when each meter arrives at the branch and then logs
all use until it leaves again.
Each branch should keep
a log
A company hiring out nuclear density meters must maintain
a register of all instruments that are available or out for hire.
But a log of use must then be kept by the person assigned
responsible at the firm to which the meter has been hired,
while it is in their possession.
NDMs available for hire registers and logs
In a similar way a firm that services meters on behalf of
other owners must keep a record of the receipt and return of
each meter they service.
Registers at firms that
service meters
The true test of a record system is whether it is possible to follow an unbroken record
trail for each meter of where it was and who was responsible for it from the time it
was obtained up to its present location.
Radiation Safety Plan
It is a condition of the user's licence that a Radiation Safety Plan is issued and implemented.
Further guidance on the preparation of radiation safety plans is available on
http://www.health.govt.nz.
Guidance Notes: NDMs – Legal requirements and responsibilities
5
SAFETY MANAGEMENT
Storage facilities (CSP15 Section 3.1)
There are storage
requirements
Both the regulations and the Code contain strict rules for
storage. This is because radioactive materials do not “switch
off” when you stop using them. The storage facility must
fulfill the requirements of Section 3.1 of the Code.
It must be secure
In particular, it must be secure. Access must be controlled by
the principal licensee so that no unauthorised person can
come in and tamper with, move, or steal, the meter.
Consideration should be given to installation of additional
security measures such as intrusion alarms, security cameras
or patrolled premises, etc.
It should be fire-resistant
It must protect the radioactive sources from any potential
damage that may affect the encapsulation or shielding. So it
should be as fire-resistant as practical, and should not contain
other dangerous materials.
NDMs should be
segregated from other
dangerous goods
Good practice suggests that nuclear density meters should not
be stored in the same area as any dangerous goods of the
following classes as specified in United Nations
recommendations on the transport of dangerous goods
(UNRTDG)[3]:
1
2.1
3
4.1
4.2
4.3
5.2
8
explosive
flammable gas
flammable liquid
flammable solid
spontaneously combustible
dangerous when wet
organic peroxide
corrosive
Is the storage appropriate?
Thus many typical industrial dangerous goods stores are
inappropriate storage locations for nuclear density meters.
Radiation shielding is
necessary
It must contain sufficient radiation shielding so that there will
be no external radiation hazard to anyone outside. The
exposure limit set in Section 3.1.3 of the Code will be
achieved if the dose rate is less than 0.5 µSv/h at all
accessible positions outside the store. This will be achieved
with a typical nuclear density meter if it is stored in its
transport case, 2 metres from any occupied position.
Signage is required
In addition to it being a labelled Type A package there must
be a sign on the door indicating the presence of radioactive
material inside (see Section 3.1.2 of the Code). This assists
emergency services in the event of a call-out. If the meter is
kept in a locked safe or cupboard, the sign can be on its door.
Guidance Notes: NDMs – Safety management
6
Responsibilities for storage (CSP15 Section 3.2)
It has been stressed already that a major safety concern with
nuclear density meters is from them going missing. The use
of appropriate storage and the conscientious return of a meter
into the correct storage facility are key safety factors. It is
essential that everyone understands and meets their
responsibilities.
Use an appropriate store
and ensure the NDM is
returned to it after use
In summary:

the principal licensee (or only licensee if there is only
one) responsible for a nuclear density meter is
responsible for ensuring that a suitable storage facility is
provided that satisfies the requirements of Sections 3.1
and 3.2 of the Code;

the owner is responsible for ensuring the facility meets
the specifications designated by the principal licensee
(see regulation 9);

every licensee who uses (or is responsible for someone
else using) a nuclear density meter is responsible for
returning the meter to its proper storage facility.
Labelling of the meter and its transport case (CSP15 Section 3.3)
Section 3.3 of the Code requires three different types of
labeling:

There must be a label on the meter indicating that it
contains radioactive material. This is required by the
regulations, and the information that the label must give
is quite specific (including the trefoil symbol, the words
“radioactive material” and the nuclide, activity and
activity date for each sealed source). The details required
are normally provided by a manufacturer’s label, but if
not, or if the manufacturer’s label is removed, then an
equivalent alternative label must be provided.
Radiation label

Both the meter and the transport case must be clearly
marked with contact details. If the meter is misplaced, it
can then be easily returned.
Contact details label

The transport case must be labelled to satisfy the IAEA
transport regulations[4]. These apply whenever a nuclear
density meter is transported by whatever means. (See the
Transport section of these Guidance notes.)
Transport labelling
Guidance Notes: NDMs – Safety management
7
Metal labels are best
The labels must be maintained in a clearly legible condition,
and replaced if they are worn or defaced. This will be more
easily achieved if the labels are made from a durable
material eg, embossed metal labels.
Accident prevention (CSP15 Section 3.4)
Sound procedures will
minimise accidents
Accidents in which nuclear density meters are run over,
especially on construction sites, happen all too frequently,
not only in New Zealand but worldwide. The circumstances
are all different, but the cause is always the same: the driver
of the vehicle did not know it was there. And once the
meter is run over, not only is it put out of action, but there is
the added inconvenience of having to treat the site of the
accident as a potential radiation hazard area. It is important
to have sound procedures to minimise the likelihood of
accidents.
There are mandatory
requirements
Section 3.4 of the Code makes two commonsense
procedures mandatory: the nuclear density meter must be
made highly visible while it is being used (eg, by the use of
brightly coloured or fluorescent cones, flashing lights, or by
the operator wearing a high visibility vest) and it must never
be left unattended.
Remove after use
At the completion of the measurement remove the meter to a
safe place, such as the user’s vehicle (and not on the ground
behind a parked roller!).
Keep other workers
informed
Other workers on the site, particularly drivers of
construction machinery, must be informed about nuclear
density meters and the problems they may present. The
safety module of initiation briefings for new workers on
construction sites should include a description of, and
warnings about, these instruments.
Maintenance and wipe testing (CSP15 Sections 3.5, 3.6 & 3.7)
Follow the instruction
manual
Maintenance should follow closely the instructions given in
the manufacturer’s instruction manual. (Insist on being
provided with this when a nuclear density meter is bought,
and keep it for future reference.) The manual will usually
provide good advice on safe ways of doing things, and what
extra equipment is needed.
Minor maintenance
Maintenance that does not involve the sources (such as
changing batteries, checking electrical circuitry, etc) must be
done with the source locked in the “closed” position where
this is appropriate. The meter should be handled for no
longer than is necessary, but there are no other precautions
required, as long as no source is exposed.
Guidance Notes: NDMs – Safety management
8
Any work involving inspecting, testing or cleaning the
sources, or maintenance of the source movement mechanism,
may only be done by a licensee (see Section 3.5 of the Code).
Maintenance of source
movement mechanism
Regular inspections and source wipe tests are required by the
Code to ensure the integrity of the encapsulation[5] of the
radioactive material. Note that the schedule in 3.6.1 of the
Code is the minimum required. Additional inspections are
required if there is any suspicion of damage to the
encapsulation. If a nuclear density meter is subjected to
particularly rugged or abrasive conditions, an inspection and
wipe test may be justified at each regular maintenance. Any
time the source housing is cleaned to remove a build-up of
soil or dust it should be inspected and appraised to determine
whether a wipe test is warranted.
Regular inspections and
wipe tests are required
When doing an inspection and wipe test the following
procedures should be followed:

always refer to the instruction manual. If you do not have
one, and it is not possible to get one, then advice should
be obtained from ORS about safe procedures for your
type of meter;

always inspect the source housings for any sign of
damage before cleaning;

look for any distortion from forcing the source, or
abrasive wear, corrosion, etc;

moisten a cotton bud and thoroughly wipe the source
housings;

without touching the cotton bud, either seal it in a plastic
bag for sending to a suitable laboratory for counting, or
hold it as close as possible (without touching) to a
suitable radiation survey meter (see p. 13 for more
information).

enter in the records for that meter that an inspection and
wipe have been done.
Normally no radiation should be detected. Section 3.8.1 of the Code specifies a
maximum activity that can be accepted, but if there is any detected at all ORS should
be consulted.
Withdrawal from use (CSP15 Section 3.8)
Once there is any indication that there is a problem with the
source, the meter should be withdrawn from service. The
two best indicators of source integrity are wipe tests and age.
If there is any problem with
encapsulation the NDM
should not be used
Guidance Notes: NDMs – Safety management
9
What is the upper limit for
leakage?
If a wipe test of a radioactive source removes more than
0.2 kBq of radioactive material[6] then the meter must be
withdrawn from service and either disposed of or sent to an
authorised service agent for replacement of the source.
Transport of a leaking
source
Whenever a meter with a source known to be leaking is
freighted anywhere it must be wrapped carefully in plastic
before placement in the freight container, and a label
attached indicating the leaking source.
Obsolete NDMs should be
withdrawn from use
While the external encapsulation of a radioactive source
may appear to be durable and in good condition after many
years of use, there is no means of determining the condition
of the internal radioactive material, particularly after it has
been subjected to years of intense beta or alpha radiation.
The material used for encapsulation of sources in nuclear
density meters is known to lose its retention qualities with
the passage of time. Most nuclear density meters are
withdrawn from use because they are obsolete before about
20 years from the date of manufacture. However, ORS
strongly recommends that all sources in nuclear density
meters continuing in operation be withdrawn from use and
disposed of before 30 years from manufacture.
Decommissioning
There are rules for
decommissioning
Nuclear density meters may be decommissioned for any
number of reasons. They may be obsolete, damaged and
uneconomic to repair, or just surplus to requirements.
Because of the radioactive sources in a meter, the owner is
not at liberty to dispose of it at will or by just abandoning it.
If for any reason a nuclear density meter is no longer
required, then the owner has four options:
It can be stored – with a
licensee

the meter can be held in storage under the control of a
licensee.
While this arrangement can continue
indefinitely as long as there is a licensee responsible for
it, there is a risk of the meter being “forgotten”.
Therefore ORS strongly recommends that it is sold or
disposed of;
It can be stored – without a
licensee

in the absence of a licensee, the owner must store the
meter to the satisfaction of the Director-General of
Health;
It can be sold

the meter may be sold or exported (see p. 1);
It can be disposed of

it may be disposed of as waste in an approved way (see
Section 3.9.1 of the Code).
Guidance Notes: NDMs – Safety management
10
For further advice on how to dispose of a meter contact ORS.
Remember that if it is transferred to anyone else either for
use or disposal then the present owner must apply to ORS for
a Consent to do so.
Contact ORS for more
advice
Safety audits (CSP15 Section 3.10)
Safety procedures only work if everyone follows them, and
record systems only work if they are kept up to date. It does
not take much of a gap in a set of records before the record
system becomes dysfunctional, and before long nobody
bothers to keep them. The reason for a safety audit is to
make a routine check that everyone is following the rules.
Good record keeping and
safety procedures are
imperative
The safety audit should be assigned to an individual at each
establishment who should systematically work through the
records for each meter and verify compliance with the Code.
Who is responsible for the
safety audit?
The easiest way to do this is to have a check list. Each meter
should either be sighted in storage or verified as being with
the person who has signed it out. All current entries in the
use log must be verified as correct. The safety audit should
also verify that placarding and documentation requirements
are being complied with (see the Transport section of these
Guidance notes).
What should the safety
audit cover?
Anything found during the audit that is not satisfactory
should be noted with details of remedial actions.
Note any remedial actions
The check list should be completed, signed, and filed so that
when ORS requests a compliance monitoring inspection there
is evidence that the safety audits have been done.
File the check list
Section 3.10 of the Code requires the internal safety audit to
be carried out at least annually. An audit once a year is
satisfactory for an organisation with only one or two nuclear
density meters which are always operated from and returned
to the same base. But a firm with several meters, or meters
frequently transported between branches, should conduct
audits sufficiently often to reveal that a meter is missing
before tracing it becomes too difficult. For such firms,
monthly audits are recommended.
Audits must be performed
regularly
Guidance Notes: NDMs – Safety management
11
OPERATOR SAFETY (CSP15 SECTION 4)
Safety during normal use
Keep exposures as low as
possible
The main safety concern with nuclear density meters is
either loss of a meter or damage to the radioactive sources.
However, even in routine normal use a meter is continuously
emitting a small amount of radiation.
This is not
particularly hazardous, but the exposure to it can be
minimized by taking a few commonsense precautions. (It is
a requirement of regulation 18 that exposure to radiation
must always be the minimum practicable.) These rules
should be followed:
Keep the source “closed”
whenever possible

If the meter is of the type that has a source on the end of
a rod that extends into the medium being measured the
source rod should always be locked in the “closed” or
“off” position at any time other than during a
measurement. The source is well shielded when it is
either in the meter or in the ground. Even when moving
the meter from one test hole to another nearby,
withdraw the source into the meter before moving it. ·
Keep at a distance

As far as practical keep everyone not involved in taking
measurements at least 3 metres away from the meter. At
this distance the radiation from the source, even
unshielded, is negligible.
Use by an unlicensed person (CSP15 Section 4.2)
Use under supervision or
instructions of a licensee
The responsibilities of a licensee for anyone using a nuclear
density meter under their supervision or instructions have
already been covered (see p. 3).
Information must be given
to an unlicensed user
If you are asked to use a nuclear density meter and you do
not have a licence, then you should have the following
information in writing: the name of the licensed person who
is responsible for safety while you are using the meter and
their contact details in case there is a problem of any sort, as
well as procedures to follow in case of an emergency. Make
sure that you understand what the radiation hazards are and
how to use the meter safely.
Advice must be given
directly by the licensee
Written instructions must be provided by the licensee. It is
important that the safety message does not get “watered
down” by being passed on from one unlicensed user to
another.
Guidance Notes: NDMs – Operator safety
12
Personal monitoring (CSP15 Section 4.3)
Nuclear density meters are designed so that under normal use
the amount of radiation emitted is very small. If the user is
never exposed to the unshielded source (and this is what is
intended to happen if the instrument is used correctly) there
is insufficient radiation to warrant personal monitoring. This
is why the Code does not make the wearing of a personal
monitor mandatory unless the use involves extensive dealing
with unshielded gamma sources (such as wipe-testing or
servicing). If required personal monitoring services are
available commercially.
Personal monitoring is not
normally required
Radiation survey meters
A “thin window” Geiger Muller (GM) type radiation survey
meter is capable of detecting alpha and beta radiation. An
instrument of this type is therefore useful for screening wipe
tests. It will not indicate the activity of the wipe, but a result
which is at background level only is sufficient to show a
clean test. Routine calibration should be carried out in
accordance with the instruction manual provided.
What sort of radiation
meter can be used?
A survey meter is also a useful teaching aid when instructing
someone in the safe use of a nuclear density meter. It gives a
clear indication of the difference in radiation dose rate when
the source is exposed and unexposed, and how quickly the
dose rate reduces with distance.
A radiation meter has other
uses
Because the external radiation hazard is not large, and there
are alternative methods of analysing wipe tests, the purchase
of a survey meter, while recommended, is not mandatory.
Contact ORS for advice on what type to get.
Purchasing a survey meter
Guidance Notes: NDMs – Operator safety
13
ACCIDENTS, LOST SOURCES, AND EMERGENCIES
Accidents (CSP15 Section 5.1)
There are a range of
accident scenarios
Around the world one of the most common types of accidents
involving radioactive sources has been the running over of
nuclear density meters by heavy construction machinery. New
Zealand is no exception. Nuclear density meters have also
been damaged in transport accidents. For such a portable type
of instrument, almost any conceivable accident scenario is
possible. Usually the encapsulation of the radioactive sources
remains intact after the accident and there is no spread of
contamination. However, the consequences of a contamination
incident totally justify the precautions specified in the Code.
Always assume that damage to the radioactive source encapsulation and possible
leakage of radioactive material may have occurred after every accident which results in
substantial mechanical damage to a nuclear density meter. As soon as possible a
source inspection and wipe test must be carried out to confirm or rule out such damage.
Use the following procedure:
Accident procedure
Note: Life saving actions or injured persons should always
take precedence over the radiation hazard. NRL can be
contacted at any time if there is any doubt as to how to
respond to the incident (NRL Duty Officer 021393632).
1
Establish a clear zone of about 3 m radius around the
damaged meter.
2
The licensee responsible for the meter at the time should
be called if not on site.
3
The licensee, or another person trained in these accident
procedures, should inspect the meter to assess the degree
of damage. An immediate wipe test should be carried out,
and if a GM meter or similar instrument is available at the
site, it should be immediately assessed. In the absence of
a GM meter, the wipe should be sent for assessment as
soon as possible.
4
Retract the source rod into its “closed” position if possible,
if this was extended at the time of the accident.
5
Whether or not any release of radioactive material is
indicated, the damaged instrument and any debris should
be placed inside a large plastic bag and sealed with
adhesive tape. In the absence of a plastic bag it should be
placed on a sheet of plastic, wrapped in the plastic and
sealed with adhesive tape. A warning label should be
attached to the package. The external radiation dose
received in the short time expected for the wrapping is of
much less concern than the need to contain any
radioactive contamination, no matter how unlikely its
occurrence. If the source rod is jammed outside the
shielding, it should be left as is within the wrapping, but
care should be taken to minimise handling close to the
source, and its position within the wrapping should be
noted.
Guidance Notes: NDMs – Accidents, lost sources, and emergencies
14
6 The wrapped instrument should then be transferred to a
safe place.
7 ORS must be advised of the accident as soon as
reasonably practicable, and the commercial agent should
also be contacted for advice.
Before further transport can be undertaken, the packaging
should be re-evaluated and probably adapted to ensure
compliance with transport requirements, particularly in
relation to external radiation dose rates if the gamma source
is initially unretracted.
Before moving the NDM
again, check the packaging
In order to follow the recommendations above, the
instrument’s transport box should contain:
What items should be
readily available?




cottonwool buds or swabs for wipe tests
a large plastic bag
a roll of adhesive tape
a warning label
Lost sources
The loss of any radioactive source can have serious
consequences. Once it is lost it is no longer under the control
of anyone responsible for its safety. Once equipment
containing radioactive sources is dismantled it is not evident
which parts are radioactive, and they may be scavenged
unknowingly.
The consequences of
losing an NDM can be
serious
By following the requirements in the Code and the advice in
these Guidance notes on security in storage and during
transport and proper record keeping, the risk of loss will be
minimised.
How to minimise the risk of
loss
If a nuclear density meter is in any way lost from the control
of the licensee responsible for it, the licensee must take
immediate action to locate and recover it. ORS must be
notified of the loss as soon as reasonably practicable and no
later than 7 days of such an occurrence and of the actions
taken. (This is a requirement of regulation 11(2)).
ORS must be notified
Fire and civil defence emergencies (CSP15 Section 5.2)
Every owner should have a manual of procedures to be
followed in the case of an emergency, including evacuation
from buildings, dealing with medical emergencies,
earthquakes, etc. This manual must have a section dealing
with procedures covering emergencies involving nuclear
density meters.
Every company’s
emergency handbook must
have a section on NDMs
Guidance Notes: NDMs – Accidents, lost sources, and emergencies
15
Responsibilities must be
assigned
In each case the procedure must establish who is
responsible for: ·

the security of any meter (if the storage building has
been damaged); ·

the safety of any meter (if there may be damage to the
meter itself).
This will usually be the licensee but procedures must
cover any eventuality.
Guidance Notes: NDMs – Accidents, lost sources, and emergencies
16
TRANSPORT
Further guidance on the requirements for transporting radioactive material is available at
http://www.health.govt.nz
Guidance Notes: NDMs – Transport
17
REFERENCES
1
Radiation Protection Act 1965. Govt. Print., Wellington.
2
Radiation Protection Regulations 1982. Govt. Print., Wellington.
3
UN recommendations on the transport of dangerous goods (UNRTDG) - 11th
revised edition, 1999.
4
IAEA regulations for the safe transport of radioactive material. 2009 ed.
Vienna: International Atomic Energy Agency. TS-R-1.
5
Radiation protection - sealed radioactive sources - general requirements and
classification. Geneva: International Standards Organization. ISO 2919:1999.
6
Radiation protection - sealed radioactive sources - leakage test methods. Geneva:
International Standards Organisation. ISO 9978:1992.
7
IATA dangerous goods regulations. 40th ed. Quebec: International Air Transport
Association, 1999.
8
Land Transport Rule: dangerous goods 1999. Wellington: Land Transport Safety
Authority, 1999.
9
Transport of dangerous goods on land. Wellington: Standards New Zealand. NZS
5433:1999.
10
1990 recommendations of the International Commission on Radiological Protection.
Oxford: Pergamon Press, 1991. ICRP publication 60.
18
APPENDIX
UNITS OF MEASUREMENT
Units of radioactivity
The atoms of materials that are radioactive are continually undergoing nuclear
transformations that result in the emission of radiation (eg, gamma rays, alpha particles, beta
particles, neutrons). The amount of radioactivity is specified in terms of how many nuclear
transformations occur during a given time. This is called the activity.
The SI (the internationally accepted) unit of activity is the becquerel (Bq). A quantity of
radioactive material that has an average rate of one transformation per second has an activity
of 1 becquerel (1 Bq).
The becquerel is a very small amount of activity and most radioactive sources have activities
where many millions or more transformations occur per second. Hence multiples of
becquerels are commonly used in describing radioactive sources.
In the case of nuclear density meters and their safe use, the following multiples of becquerels
are commonly used:
1 kilobecquerel (1 kBq)
1 megabecquerel (1 MBq)
1 gigabecquerel (1 GBq)
=
=
=
1 thousand (1000 or 103 ) Bq
1 million (1 000 000 or 106 ) Bq
1 thousand million (1 000 000 000 or 109 ) Bq
Many radioactive sources will have their activities stated in terms of an older unit called the
curie (Ci). This is a relatively large unit and often its sub-multiples are used.
Both units are still in use, and this is likely to continue until the use of curies is completely
phased out. Useful conversions are:
1 nCi
1 µCi
1 mCi
1 Ci
=
=
=
=
37 Bq
37 kBq
37 MBq
37 GBq
1 kBq
1 MBq
1 GBq
=
=
=
27 nCi
27 µCi
27 mCi
Note 1: The activity of radioactive material will decrease over time due to the decay of the
radioactive material.
Note 2: A statement of activity, in becquerels or curies, gives no indication of the physical
size of the radioactive material.
Guidance Notes: NDMs – Appendix: Units of measurement
19
Units of radiation dose
In radiation protection it is the risk of biological effects of the radiation that is of concern.
These biological effects are related to the amount of energy absorbed from the radiation by
the tissue, organ or body. The absorbed energy per mass of the tissue, organ or body,
multiplied by a factor dependent on the type of radiation, is called the equivalent dose. The
SI unit of equivalent dose is the sievert (Sv). One sievert is a large dose and more commonly
equivalent doses are expressed in terms of the sub-multiples: millisieverts (mSv) and
microsieverts (µSv).
There is an older unit for equivalent dose that is still sometimes used, called the rem.
Conversion from rem to sieverts can be made using:
1 mrem
1 rem
10 rem
100 rem
=
=
=
=
10 µSv
10 mSv
100 mSv
1 Sv
Dose rate is measured in units of Sv/hour or mSv/hour, etc.
Radiation dosimetry is a complex subject and a comprehensive treatment of it is beyond the
scope of these Guidance notes. Precise definitions and descriptions of the technical concepts
can be found in ICRP publication no. 60[10].
Guidance Notes: NDMs – Appendix: Units of measurement
20
CROSS-REFERENCE INDEX
These Guidance notes give practical advice for compliance with radiation protection
legislation and the relevant Code, CSP15. The references to the legislation in this index are
not always directly cited in this document or the Code, but do provide the regulatory authority
for the Code's requirements and the Guidance notes' recommendations.
The references are from these Guidance notes: safe practice for the use of nuclear density
meters to:
 Code of safe practice for the use of nuclear density meters, CSP15 (ORS, June 2000);
 Radiation Protection Regulations 1982;
 Radiation Protection Act 1965;
Guidance notes
Page No./Contents
LEGAL REQUIREMENTS AND
RESPONSIBILITIES
1
Consents for import, export, sale
and ownership
2
Licences to use radioactive material
3
Use by an unlicensed person
3
Responsibilities of owner
4
Equipment registers and records of
use
5
Radiation Safety Plan
SAFETY MANAGEMENT
6
Storage facilities
7
Responsibilities for storage
7
Labelling of the meter and its
transport case
8
Accident prevention
8
Maintenance and wipe testing
9
Withdrawal from use
10 Decommissioning
11 Safety audits
OPERATOR SAFETY
12 Safety during normal use
12 Use by an unlicensed person
13 Personal monitoring
13 Radiation survey meters
ACCIDENTS, LOST SOURCES
AND EMERGENCIES
14 Accidents
15 Lost sources
15 Fire and civil defence emergencies
TRANSPORT
NRL C15
Section
Regulations
No.
Act
Section
12
13
13
4.2
2
3.1
3.2
3.3
3.4
3.5, 3.6, 3.7
3.8
3.9
3.10
4
4
4.2
4.3
9(1), 9(4)(C), 9(2)
16(1)
9, 11
12, Second schedule
Second schedule
13 (3)
14, 15
12, 13, Second schedule
11, 18
13(1)
20
20
5.1
11(2)
5.2
6
3
Guidance Notes: NDMs – Cross-reference index
21